This invention relates to improvement in mattress innerspring units and, more particularly, to a means for preventing spin-out of cross helicals therein and for stiffening or firming an innerspring unit or a portion of the unit, such as the longitudinal side border regions.
Mattress innerspring units are generally formed of a plurality of coil springs arranged in side-by-side relation in a plurality of parallel rows between upper and lower border wires. The border wires are generally connected to the coil springs at the perimeter of the unit. It has been the practice to interconnect the coil springs of a row at their upper and lower terminal convolutions, respectively, with a plurality of helical coils (cross helicals) extending transversely across each of the rows of the unit. The coil springs are interconnected by rotating or threading each cross helical spirally about its major axis until it is extended transversely of each of the rows lacing together the terminal convolutions of the coil springs along the adjacent edges of such convolutions. The terminal convolutions of coil springs are generally closed circular loops which may have offset portions on opposite sides which offsets provide a straight portion about which the cross helical laces.
Once the cross helicals are in position they have a tendency to "spin-out", that is, unwind from the innerspring unit. To eliminate this action, it has been the practice to deform the cross helicals in various manners. For example, each end of a cross helical can be given a reverse twist, which is the doubling back of the end portion of the helical on itself. Alternatively, a cross helical, at portions of its length between interlaced convolutions of coil springs, can have several of its convolutions rotated about an axis transverse to the axis of the cross helical, as shown for example in U.S. Pat. No. 3,685,062. A further method of eliminating cross helical spin-out is to crimp or compress portions of each cross helical near its opposite ends to frictionally engage the helical with the laced adjacent terminal convolutions of the coil springs of the first or second outermost row of the innerspring unit, as described in U.S. Pat. No. 3,653,082. This latter method has the further advantage of stiffening the mattress innerspring unit in the area in which the cross helicals have been crimped. Although these methods have reduced spin-out, none have completely eliminated cross helical spin-out.
It is desirable that mattress innerspring units be firm which firmness is related in part to the number of coil springs in the innerspring unit, i.e. the coil count. It is also desirable that the longitudinal side borders of mattress innerspring units be firmer than the center or end portions. The crimping of helicals about the end convolution offsets of coil springs at the sides of a unit, as described also in U.S. Pat. No. 3,653,082, does increase firmness at the sides of the innerspring unit. An even greater degree of firmness, however, would be advantageous. It may also be desired to provide additional firmness at the other regions of the innerspring unit, such as the longitudinal mid-region of a wide mattress.
It is therefore an object of the present invention to provide a means for a mattress innerspring unit which will reduce cross helical spin-out and increase the firmness of the unit.
It is another object to provide a retention and support strip which may be secured in such a manner to an innerspring unit at the point where the cross helicals interlace adjacent coil springs to reduce cross helical spin-out and increase the firmness of the unit.
It is a further object to provide a mattress innerspring unit containing cross helicals interlacing adjacent coil springs where a retention and support strip is positioned along the upper and lower terminal convolutions of coil springs in at least one row (such as the first, second, and/or third rows of springs adjacent to the side border wires of the unit) which strip grips the adjacent portions of the cross helicals and which helicals frictionally engage the terminal convolutions of the springs in such rows so as to reduce helical spin-out, provide additional firmness to the unit and bridge the springs in these rows.